The valve drive system emerging from EP 1 143 120 A2 is considered to be the closest prior art. Here, a cam follower is connected on one end to a head of a support element in an articulated way. Coupling pistons that can be displaced, for the coupled case, by the force of a compression spring directly into a borehole of the head of the support element sit, in the decoupled case, in bushings of side walls of the cam follower. On the inside at the ends, the coupling pistons contact slides of the borehole of the support element that can be loaded, for a decoupled case, on their inner ends with hydraulic medium and that exert a force outward in the radial direction onto the coupling pistons. Thus, there is a complicated slide assembly. In the decoupled case, the cam follower detached from the head of the support element pivots in the direction of the support element, wherein its restoring position in the cam direction is realized by a helical compression spring (lost-motion spring) enclosing the support element and sitting in the cylinder head on one end.
For the construction noted above, it is disadvantageous that this construction cannot perform partial strokes and thus gives only limited variability. In addition it has been determined that through the arrangement of the coupling pistons in the pivoting cam follower, its mass moment of inertia is increased unnecessarily and the cylinder head of the combustion engine must be changed for integration of the helical compression spring. In addition, in the decoupled mode there is the risk that the cam follower pivots so far that the borehole of the head of the support element is exposed and thus the slides are no longer secured.